In order to increase the efficiency (G/T) of an antenna system it is possible to combine a plurality of antennae to form a large antenna, the signals of the individual antennae being superimposed to form a common signal. It is thereby possible to receive even weak signals which could not be received with sufficient quality by means of single smaller antenna. The gain of planar antennae can be increased, for example, by connecting a large number of radiating elements by means of a common coupling network to a common feed point. Because the radiating elements cannot be arranged with any desired density side-by-side in one plane the length of lines between radiating elements and coupling point constantly increases with a constantly increasing number of radiating elements, so that the loss to the antenna caused by the coupling network becomes unacceptable.
Known from U.S. Pat. No. 5,475,394 is a planar antenna which is composed of four individual smaller planar antennae. Each of the four planar antennae forms a quadrant of the large square antenna, each of the four planar antennae having a feed network to supply their radiation elements. To achieve the highest possible directivity the four feed points of the four individual planar antennae are coupled at equal amplitude and in an in-phase and low-loss manner to a common coupling point or feed point by means of a waveguide system. Also known from U.S. Pat. No. 5,475,394 is a planar antenna in which two planar antennae are arranged one behind the other and each consist of four smaller planar antennae, which in each case form quadrants of a square. The feed points of the four planar antennae disposed in one plane are in each case connected, as described above, to a common coupling point or feed point by means of their own waveguide system.
A disadvantage of the planar antennae with waveguide configurations known from U.S. Pat. No. 5,474,394 is that, to achieve the best possible HF characteristics, the waveguide structure would have to be manufactured in one piece. The known technical procedures for achieving this are all complex and expensive. The fundamental problem lies in removing the core of relatively complex waveguide structures which in practice are produced by connecting three or more partial elements. Core removal is conventionally carried out by the melt-out method. An advantageous splitting of the waveguide system into individual components which are subsequently connected is also complex and expensive because, in view of the selected waveguide structure and the dominant mode associated therewith (H10 mode or TE10 mode in waveguides with rectangular cross-section) the wall currents are interrupted at the cut edges, causing undesirable reflections which can seriously impair the entire complex power distribution in the waveguide network. The contact problem arising here between the partial components to be connected makes a low-cost solution impossible.
Also known from U.S. Pat. No. 5,243,357 is an antenna for simultaneous reception of two orthogonal electromagnetic waves in which the radiating elements are coupled to a common coupling point by means of a waveguide configuration. The waveguide of the waveguide configuration has a square cross-sectional area since otherwise the two orthogonal electromagnetic waves could not be propagated therein. The above-mentioned disadvantages, as present in the case of the antenna according to U.S. Pat. No. 5,475,394, also apply to this antenna.
Known from European Patent Application EP 0569017 is a waveguide configuration in which a waveguide consists of two parts each of which has an elongated recess in one of its flat sides, the recesses together forming the cavity of the waveguide. Known from Yoshiki K et al: “A broadband planar antenna employing waveguide parallel feed circuit”, 1994, IEEE, pp. 1862-1865, XP000546058 ISBN: 0-7803-2009-3 , is a planar antenna in which a plurality of radiating elements are fed via a complex waveguide configuration. The essay does not, however, disclose the concrete structure of the waveguide configuration.
It is therefore one object of the present invention to provide a generic planar antenna with a waveguide configuration for in-phase coupling of the coupling points of the individual planar antennae to the common coupling point, which planar antenna is, on the one hand, simple in structure and therefore economical to mass produce with suitable manufacturing technologies and, on the other hand, ensures optimum, reflection-free wave guidance, even taking account of manufacturing tolerances.
Other objects of the present invention shall become apparent in light of the specification and claims.